IE44164B1 - Improvements in or relating to intermediate frequency converters - Google Patents

Description

The invention relates to intermediate frequency converters for the change of an intermediate frequency from the value used in one information transmission system in particular a radio relay system with a first predetermined intermediate frequency, to another value used in another information transmission system having a different intermediate frequency, and vice versa.

For example, in radio relay devices for TV transmission or for carrier-frequency communications handling up to 1,800 speech channels, the intermediate frequency of 70 MHz is commonly used, whereas radio relay devices for 2,700 speech channels commonly employ an intermediate frequency of 140 MHz, a high frequency being required on account of the greater band-width needed in this latter case.

In order to achieve optimum exploitation in such radio relay links provided within a communications network, the need may exist where necessary to conduct a signal with 1,800 speech channels or a television programme via a radio relay link which is designed for 2700 speech channels. If the principle of IF switchthrough is to be maintained in such cases, special measures must be provided to ensure that it is possible for devices operating at the intermediate frequency of 70 MHz and devices operating at the intermediate frequency of 140 MHz to directly co-operate with one another . The possibility fundamentally exists of 416 4 - 3 switching through a signal comprising 1800 speech channels to a radio relay link with 2700 speech channels by transferring the signals in their basic frequency level, with demodulation and remodulation processes. However, this would give rise to additional noises and distortions. Switch-through at the IF level is particularly suitable for the transmission of TV programmes, in order to avoid any pulse distortions from use of a modem.

In addition to the high requirements involving freedom from harmonics and freedom from distortion, an intermediate frequency converter of this type is required to be as economical as possible in order to be economically viable.

One object of the present invention is to provide an intermediate frequency converter of the type described in the introduction, which meets the high requirements for quality of a wide-band conversion, and yet allows for the possibility of a selective reversal of the conversion direction without re-equipment of the intermediate frequency converter, such as is normally required for reversal of the conversion direction by use of additional components and circuits.

The invention consists in an intermediate frequency converter for transforming a first intermediate frequency signal used in one information transmission system to a second intermediate frequency signal used in another such system, in which said first intermediate frequency signal is fed to an upwards converter for mixing with the output of a first converter oscillator to produce a high level intermediate signal which is fed to a downwards converter for mixing with the output of a second converter oscillator in order to produce said second -i 16 4 - 4 intermediate frequency signal at its output, and to provide for a selective reversal of the conversion direction in which said second intermediate frequency signal is fed to said upwards converter to produce said high level intermediate signal, which is then fed to said downwards converter to produce said first intermediate frequency signal at its output, the converter oscillators or their crystals are interchangeable and the frequency characteristics of their associated selection means retuned appropriately, in accordance with the required conversion direction.

The invention is based on the fact that a direct conversion from a first given intermediate frequency to a second given intermediate frequency is generally impossible, because harmonics of the incoming signal frequencies would fall into the outgoing operating band. The same problems may also occur when the direction of conversion is reversed.

These difficulties can be overcome by means of the selected double conversion via a higher intermediate frequency than either of the system i.f. frequencies.

In addition, the invention is based on the recognitioh that a reversal of the conversion direction can be effected with simple means without additional components or circuit parts when the highermost intermediate frequency is predetermined independently of the direction of the conversion, because the re-equipment of the intermediate frequency converter is then basically confined to exchanging the frequencies of the converter oscillators in respect of their assigned converters.

In a preferred embodiment each assembly is divided into two sub-assemblies, both comprising a converter - 5 sub-assembly and an oscillator sub-assembly. Both assemblies are combined to form a double assembly, arranged back-to-back in a housing and separated by a metallic screen. The two sub-assemblies of each assembly are each screened from one another by a supply line duct that is formed by metallic partition walls.

In an advantageous embodiment a radio relay system operating with an intermediate frequency of 70 MHz is coupled to a radio relay system operating with an intermediate frequency of 140 MHz and vice versa, using a high level intermediate frequency at the output of the upwards converter which has a value of 448 MHz. Consequently with an input i.f. signal of 70 or 140 MHz, the frequency of the first converter oscillator is fixed at 518 or 588 MHz respectively, and the second converter oscillator is fixed at 588 or 518 MHz respectively.

The high level intermediate frequency offers a good freedom from interference, and still allows the use of conventional components and construction principles.

As the lower difference frequency is used in both conversions, so that the conversion to the lower difference frequency is carried out twice, consecutively, the intermediate frequency signal at the output has the normal signal frequency distribution, and is not inverted.

In order to ensure a high long-term frequency stability for the converter oscillators with a relatively low outlay, they preferably each consist of a quartz oscillator with a subsequently connected frequency multiplier.

In one preferred exemplary embodiment each frequency multiplier has a multiplication factor of 5, - 6 as by this means any interference spectrum which occurs next to the required signal frequency band has a sufficient frequency spacing therefrom.

The invention will now be described with reference to the drawings, in which:Figure 1 is a block schematic circuit diagram illustrating the construction of one exemplary embodiment of an intermediate frequency converter constructed in accordance with the invention; Figure 2 is a schematic front view of a double assembly which incorporates the intermediate frequency converter corresponding to Figure 1; and Figure 3 is a cross-sectional view on the line A-B of Figure 2.

In the embodiment illustrated in Figure 1 an input assembly BGl is coupled to an output assembly BG2. The input-end assembly BGl of the intermediate frequency converter, at whose input the input-end signal with an intermediate frequency fzl is present, consists of two sub-assemblies, an upwards converter AU1 and a first converter oscillator U01. The output-end assembly BG2 consists of two sub-assemblies, a downwards converter AU2 and a second converter oscillator U02. The inputend signal with the intermediate frequency fzl passes via an attenuating element Dl and a filter TP, which serves for the input selection, to a mixer Ml, to which is fed via a second input an oscillation of frequency fl from the first converter oscillator U01. The function of the attenuating element Dl is to damp the level of the input-end signal to ensure as weak as possible an operation in the mixer Ml, so that there is a reduction in any undesired, yet unavoidable 1 G ri - 7 interference spectral lines that are produced in the execution of the mixing process. The output of the mixer Ml is fed to an amplifier VI, which amplifies the high level intermediate frequency fz3 oscillation produced in the mixer Ml and subsequently feeds the latter via a bandpass filter BP1 which suppresses undesired mixed products outside the operating band, and has its output connected to an attenuation element D2 which feeds the oscillation with the high intermediate frequency fz3 in decoupled fashion to the input of a downwards converter AU2.

The downwards converter AU2 itself consists at the input end of a mixer M2 whose output is connected to the input of a bandpass filter BP2 which feeds an amplifier V2. The oscillation produced by a second converter oscillator U02, having the frequency f2 is applied to a second input of the mixer M2. The band-pass filter BP2 serves to suppress undesired mixed products that lie outside the operating band and occur during the mixing process. The converted, input-end signal is present at the output of the amplifier V2, which here represents the output of the intermediate frequency converter, with the intermediate frequency fz2.

The converter oscillators U01 and U02 each consists of a quartz oscillator 01 and 02 respectively with subsequently connected respective frequency multipliers FV1 and FV2. Each of the two frequency multipliers itself consists of a multiplier stage VS1 and VS2 respectively, whose output feeds a respective selective amplifier SVl or SV2.

In a preferred embodiment an intermediate frequency converter transforms an input intermediate frequency fzl - 8 of 70 MHz to a high level intermediate frequency fz3 of 448 MHz, and resultant output-end intermediate frequency fz2 is 140 MHz, the frequency fl of the first converter oscillator UOl being 518 MHz, and the frequency f2 of the second converter oscillator U02 being 588 MHz.

Taking into consideration the multiplication factor n = 5 of the multiplier stages VS1 and VS2, the frequency of the quartz oscillator 01 is 103.6 MHz and that of the quartz oscillator 02 is 117.6 MHz. If the intermediate frequency converters are to carry out the conversion in the opposite direction, an intermediate frequency signal with the frequency fz2 = 140 MHz is thus present at the input, and if the output-end signal is to have the intermediate frequency fzl = 70 MHz, this can be achieved in a simple fashion if the oscillator sub-assemblies, thus the first converter oscillator UOl and the second converter oscillator U02, are simply exchanged with one another. . In addition, in this case it is necessary to retune the filter TP of the upwards converter AU1 and the band-pass filter BP2 of the downwards converter AU2. The retuning of these selection means is indicated by solid arrows at the given points in Figure 1.

Instead of exchanging the entire converter oscillator sub-assemblies, it is also possible to simply exchange the quartz crystals of the quartz oscillator with one another. In this case, however, it is necessary to design the selective amplifiers SVl and SV2 to be retunable, as indicated by broken-line arrows at the relevant points.

In order to achieve a space-saving construction, whilst simultaneously ensuring mutual decoupling, the two assemblies BG1 and BG2 in accordance with Figure 1 - 9 are preferably combined back-to-back to form a main assembly. As shown by the housing sketch in Figure 2, the assembly BG1 is arranged in the right-hand half and the assembly BG2 in the left-hand half of a double assembly housing. The assemblies themselves are merely indicated by circuit boards LPl and LP2, shown by broken lines. The circuit boards LPl and LP2 are separated from one another by a metallic screen AS. A frame R of the double assembly housing carries removable covers Dkl and Dk2. For the connection between the output of the upwards converter AU1 and the input of the downwards converter A02, the circuit boards LPl and LP2 and the metallic screen As are provided with aligned openings o, through which passes a line connection lo. The input of the assembly BG1 is in the form of a coaxial socket KB1 and the output of the assembly BG2 is a coaxial socket KB2 on the lower narrow side of the frame R.

As can be seen from the section on the line A-B of Figure 2, shown in Figure 3, the circuit boards LPl and LP2 are divided up to form sub-assemblies as represented by rectangles in Figure 1. A longitudinal duct R separates the two sub-assemblies» and is positioned between transverse metallic partition walls TW1 and TW2, which together define the duct F that serves to receive supply lines for the adjoining sub-assemblies. The connection lines which serve to supply the oscillator output oscillations to the associated mixers are reference 11 and 12. The partition walls TW1 and TW2 are connected by conductive links passing through the circuit boards LPl and LP2 and provided with a lowimpedance coupling connection therebetween via respective spring plates FB contacting the links which penetrate 416« - 10 the boards. The partition walls TW1 and TW2 are provided with low-impedance connections to the covers DK1 and DK2, and to the frame R, via spring strips ELI and FL2 which serve to ensure an effective completion of the screening.

Claims (5)

1. An intermediate frequency converter for transforming a first intermediate frequency signal used in one information transmission system to a second intermediate frequency signal used in another such system, in which said first intermediate frequency signal is fed to an upwards converter for mixing with the output of a first converter oscillator to produce a high level intermediate signal which is fed to a downwards converter for mixing with the output of a second converter oscillator in order to produce said second intermediate frequency signal at its output, and to provide for a selective reversal of the conversion direction in which said second intermediate frequency signal is fed to said upwards converter to produce said high level intermediate signal, which is then fed to said downwards converter to produce said first intermediate frequency signal at its output, the converter oscillators or their crystals are interchangeable and the frequency characteristics of their associated selection means retuned appropriately, in accordance with the required conversion direction.

2. An intermediate frequency converter as claimed in Claim 1, in which the said converter is in the form of a main assembly divided into two subassemblies, each one of which includes an oscillator sub-assembly, said two sub-assemblies with their respective oscillator sub-assemblies being combined back-to-back in a common housing to form said main assembly, the respective sub-assemblies being separated by a metallic screen and the oscillator or sub-assembly being screened from the remainder by a supply line duct 4 41θ4 defined by metallic partition walls.

3. An intermediate frequency converter as claimed in Claim 1 or Claim 2, for linking a radio relay system operating with an intermediate frequency of 70 MHz to a 5 radio relay system operating with an intermediate frequency of 140 MHz, in which said high level intermediate frequency at the output of the upwards converter is 448 MHz, the frequency of the first converter oscillator being fixed at 518 MHz and that of the second converter 10 oscillator being fixed at 588 MHz when intermediate frequency signals of 70 MHz are to be applied, and the oscillator frequencies being interchanged when intermediate frequency signals of 140 MHz are to be applied.

4. An intermediate frequency converter as claimed 15 in any preceding Claim, in which said converter oscillators each consists of a quartz oscillator feeding a subsequently connected respective frequency multiplier.

5. An intermediate frequency converter substantially as described with reference to Figures 1 to 3.